Method and device for re-establishing pdcp in wireless communication system

ABSTRACT

Disclosed are a communication technique for merging IoT technology with a 5G communication system for supporting a data transmission rate higher than that of a 4G system and a system therefor. The present disclosure can be applied to intelligent services (for example, smart home, smart building, smart city, smart car or connected car, healthcare, digital education, retail, security, and safety related services, and the like) on the basis of 5G communication technology and IoT-related technology. The present invention relates to operations of a terminal and a base station in a mobile communication system. The present invention provides a method by which a terminal re-establishes a PDCP in a wireless communication system, the method comprising the steps of: receiving a message including PDCP re-establishment information on a DRB from a base station in which an RRC connection is set up; checking whether the PDCP re-establishment information includes configuration information of an SDAP layer; and determining whether to perform a PDCP re-establishment procedure for changing the DRB operating as a PDCP of a first system into a PDCP of a second system on the basis of the checking result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 17/715,839,filed Apr. 7, 2022, now U.S. Pat. No. 11,751,271, which is acontinuation of application Ser. No. 16/638,085, now U.S. Pat. No.11,330,660, which is the 371 National Stage of International ApplicationNo. PCT/KR2018/009121, filed Aug. 9, 2018, which claims priority toKorean Patent Application No. 10-2017-0101945, filed Aug. 10, 2017, thedisclosures of which are herein incorporated by reference in theirentirety.

BACKGROUND 1. Field

The disclosure relates to a re-establishment method and device based ona version change of a PDCP in a mobile communication system.

Furthermore, the disclosure relates to a method and device for aterminal to perform carrier aggregation activation without a delay upontransition from an inactive state to a connected state in anext-generation mobile communication system.

2. Description of Related Art

In order to satisfy wireless data traffic demands that tend to increaseafter 4G communication system commercialization, efforts to develop anenhanced 5G communication system or a pre-5G communication system arebeing made. For this reason, the 5G communication system or pre-5Gcommunication system is called a beyond 4G network communication systemor a post LTE system.

In order to achieve a high data transfer rate, the 5G communicationsystem is considered to be implemented in a mmWave band (e.g., 60 GHzband). In order to reduce a loss of electric waves and increase thetransfer distance of electric waves in the mmWave band, beamforming,massive MIMO, full dimensional MIMO (FD-MIMO), array antenna, analogbeamforming and large scale antenna technologies are being discussed inthe 5G communication system.

Furthermore, in order to improve the network of a system, technologies,such as an improved small cell, an advanced small cell, a cloud radioaccess network (cloud RAN), an ultra-dense network, device to devicecommunication (D2D), wireless backhaul, a moving network, cooperativecommunication, coordinated multi-points (CoMP) and receptioninterference cancellation, are being developed in the 5G communicationsystem. In addition, hybrid FSK and QAM modulation (FQAM) and slidingwindow superposition coding (SWSC) that are advanced coding modulation(ACM) schemes, improved filter bank multi-carrier (FBMC), non-quadraturemultiple access (NOMA) and sparse code multiple access (SCMA) are beingdeveloped in the 5G system.

In the 5G system, the support of various services for the existing 4Gsystem is taken into consideration. For example, most representativeservices may include enhanced mobile broad band (eMBB), ultra-reliableand low latency communication (URLLC), massive machine typecommunication (mMTC), evolved multimedia broadcast/multicast service(eMBMS), etc. Furthermore, a system providing the URLLC service may becalled a URLLC system, and a system providing the eMBB service may becalled an eMBB system. Furthermore, terms, such as service and system,may be interchangeably used.

From among the services, the URLLC service is newly taken intoconsideration in the 5G system unlike the existing 4G system andrequires the satisfaction of ultra-high reliability (e.g., a packeterror rate of about 10-5) and low latency (e.g., about 0.5 msec)conditions, compared to other services. In order to satisfy such strictrequirements, the URLLC service may need to apply a short transmissiontime interval (TTI) compared to the eMBB service. Various operationmethods using the TTI are taken into consideration.

The Internet evolves from a human-centered connection network over whichhuman generates and consumes information to Internet of Things (IoT) inwhich information is exchanged and process between distributed elements,such as things. An Internet of Everything (IoE) technology in which abig data processing technology through a connection with a cloud serveris combined with the IoT technology is emerging. In order to implementthe IoT, technical elements, such as the sensing technology,wired/wireless communication and network infrastructure, serviceinterface technology and security technology, are required. Accordingly,technologies, such as a sensor network, machine to machine (M2M) andmachine type communication (MTC) for a connection between things, arerecently researched. In the IoT environment, an intelligent Internettechnology (IT) service in which a new value is created for human lifeby collecting and analyzing data generated from connected things may beprovided. The IoT may be applied to fields, such as a smart home, asmart building, a smart city, a smart car or a connected car, a smartgrid, health care, smart home appliances, and advanced medical services,through convergence and composition between the existing informationtechnology (IT) and various industries.

Accordingly, various attempts to apply the 5G communication system tothe IoT are being made. For example, 5G communication technologies, suchas a sensor network, machine to machine (M2M) and machine typecommunication (MTC), are implemented by schemes, such as beamforming,MIMO, and an array antenna. The application of a cloud wireless accessnetwork (cloud RAN) as the aforementioned big data processing technologymay be said to be an example of convergence between the 5G technologyand the IoT technology.

SUMMARY

The disclosure provides an operation in a bearer change when a handoveror sequence number change operation occurs in the dual connectivity ofLTE and NR newly introduced in a next-generation mobile communicationsystem. In particular, the disclosure provides a change operation froman LTE PDCP to an NR PDCP through a PDCP re-establishment operation if aPDCP version change of the bearer changes is necessary and a relatedoperation thereof.

Furthermore, in a next-generation mobile communication system, in orderto provide service having a high data transfer rate and low transmissionlatency, a base station needs to rapidly configure a carrier aggregation(CA) technology or a dual connectivity (DC) technology in a terminal. Inparticular, upon transition from an inactive state to a connected state,if such transition operates similar to the existing transition from anidle state to a connected state, a lot of time is taken to newlyestablish a connection and activate a carrier aggregation. Accordingly,the disclosure proposes a method and device for a terminal to performcarrier aggregation activation without a delay upon transition from aninactive state to a connected state.

Technical objects to be achieved in the disclosure are not limited tothe aforementioned technical objects, and other technical objects notdescribed above may be evidently understood by a person having ordinaryskill in the art to which the disclosure pertains from the followingdescription.

The disclosure provides a method for a terminal to re-establish a packetdata convergence protocol (PDCP) in a wireless communication system,including receiving, from a base station, a message including PDCPre-establishment information for a data radio bearer (DRB), the basestation configured a radio resource control (RRC) connection,identifying whether configuration information for a service dataadaptation protocol (SDAP) layer is included in the PDCPre-establishment information, and determining whether to perform a PDCPre-establishment procedure for changing the DRB, operating as a PDCP ofa first system, into a PDCP of a second system based on a result of theidentification.

Furthermore, the disclosure provides a terminal re-establishing a packetdata convergence protocol (PDCP) in a wireless communication system,including a transceiver transmitting and receiving signals and acontroller configured to receive, via the transceiver from a basestation, a message including PDCP re-establishment information for adata radio bearer (DRB), the base station configured a radio resourcecontrol (RRC) connection, identify whether configuration information fora service data adaptation protocol (SDAP) layer is included in the PDCPre-establishment information, and determine whether to perform a PDCPre-establishment procedure of changing the DRB, operating as a PDCP of afirst system, into a PDCP of a second system based on a result of theidentification.

Furthermore, the disclosure provides a method for a base station tochange a radio resource control (RRC) state, including determining asecondary cell in which a cell configuration with a terminal ismaintained and transmitting, to the terminal, a control messageinformation on the secondary cell. In the RRC inactive state of theterminal, the cell configuration between the terminal and the secondarycell is maintained.

Furthermore, in the method, the control message may be a message,including a first SCell list indicative of the secondary cell andindicating the transition of the terminal to the RRC inactive state.

Furthermore, in the method, the control message may be an RRC connectionresume message including a second SCell list indicative of the secondarycell.

Furthermore, in the method, an RF synchronization and tuning operationmay be performed on the secondary cell by the terminal.

Furthermore, in the method, the secondary cell may be a secondary cellpresent within a base station with which an RRC connection with theterminal has been established or a secondary cell within a base stationpresent within a RAN paging area.

Furthermore, the method may further include transmitting, to theterminal, a message to activate a carrier aggregation (CA) with respectto a cell in which the secondary cell configuration is maintained.

Furthermore, in the method, the message to activate a carrieraggregation (CA) may include a third SCell list indicative of at leastone of the secondary cells, and may be a medium access control (MAC)control element (CE).

Furthermore, the disclosure provides a method for a terminal to change aradio resource control (RRC) state, including identifying whetherinformation on a secondary cell with which a cell configuration is to bemaintained is included in a control message received from a basestation, determining whether to maintain the cell configuration of thesecondary cell in the RRC inactive state based on a result of theidentification, and maintaining the cell configuration determined indetermining whether to maintain the cell configuration.

Furthermore, in the method, identifying whether information on asecondary cell with which a cell configuration is to be maintained isincluded may further include identifying whether the control message isa message to indicate the transition of the terminal to the RRC inactivestate and identifying whether a first SCell list indicative of asecondary cell is included in the information.

Furthermore, in the method, identifying whether information on asecondary cell with which a cell configuration is to be maintained isincluded may further include identifying whether the control message isan RRC connection resume message and identifying whether a second SCelllist indicative of a secondary cell is included in the information.

Furthermore, in the method, determining whether to maintain the cellconfiguration may further include determining whether to maintain thecell configuration based on the most recently received information if aplurality of pieces of information for a secondary cell with which acell configuration is to be maintained is identified.

Furthermore, in the method, maintaining the cell configuration mayfurther include maintaining and tuning RF synchronization for thesecondary cell.

Furthermore, in the method, the information on the secondary cell may beinformation on a secondary cell present within the base station or asecondary cell within a base station present within a RAN paging area.

Furthermore, the method may further include receiving, from the basestation, a message to activate a carrier aggregation (CA) with respectto a secondary cell in which the cell configuration is maintained, andperforming CA activation.

Furthermore, in the method, the message to activate a carrieraggregation (CA) may include a third SCell list indicative of at leastone of the secondary cells, and may be transmitted through a mediumaccess control (MAC) control element (CE).

Furthermore, the disclosure provides a base station, including atransceiver transmitting and receiving signals and a controllerconfigured to determine a secondary cell in which a cell configurationwith a terminal is maintained and transmit, to the terminal, a controlmessage information on the secondary cell. In the RRC inactive state ofthe terminal, the cell configuration between the terminal and thesecondary cell is maintained.

Furthermore, in the base station, the control message may be a message,including a first SCell list indicative of the secondary cell andindicating the transition of the terminal to the RRC inactive state.

Furthermore, in the base station, the control message may be an RRCconnection resume message including a second SCell list indicative ofthe secondary cell.

Furthermore, in the base station, an RF synchronization and tuningoperation may be performed on the secondary cell by the terminal.

Furthermore, in the base station, the secondary cell may be a secondarycell present within a base station with which an RRC connection with theterminal has been established or a secondary cell within a base stationpresent within a RAN paging area.

Furthermore, in the base station, the controller may be furtherconfigured to transmit, to the terminal, a message to activate a carrieraggregation (CA) with respect to a cell in which the secondary cellconfiguration is maintained.

Furthermore, in the base station, the message to activate a carrieraggregation (CA) may include a third SCell list indicative of at leastone of the secondary cells, and may be a medium access control (MAC)control element (CE).

Furthermore, the disclosure provides a terminal, including a transceivertransmitting and receiving signals and a controller configured toidentify whether information on a secondary cell with which a cellconfiguration is to be maintained is included in a control messagereceived from a base station, to determine whether to maintain the cellconfiguration of the secondary cell in the RRC inactive state based on aresult of the identification, and to maintain the cell configurationdetermined in determining whether to maintain the cell configuration.

Furthermore, in the terminal, the controller may be further configuredto identify whether the control message is a message to indicate thetransition of the terminal to the RRC inactive state and to identifywhether a first SCell list indicative of a secondary cell is included inthe information.

Furthermore, in the terminal, the controller may be further configuredto identify whether the control message is an RRC connection resumemessage and to identify whether a second SCell list indicative of asecondary cell is included in the information.

Furthermore, in the terminal, the controller may be further configuredto determine whether to maintain the cell configuration based on themost recently received information if a plurality of pieces ofinformation for a secondary cell with which a cell configuration is tobe maintained is identified.

Furthermore, in the terminal, the controller may be further configuredto maintain and tuning RF synchronization for the secondary cell.

Furthermore, in the terminal, the information on the secondary cell maybe information on a secondary cell present within the base station or asecondary cell within a base station present within a RAN paging area.

Furthermore, in the terminal, the controller may be further configuredto receive, from the base station, a message to activate a carrieraggregation (CA) with respect to a secondary cell in which the cellconfiguration is maintained, and to perform CA activation.

Furthermore, in the terminal, the message to activate a carrieraggregation (CA) may include a third SCell list indicative of at leastone of the secondary cells, and may be transmitted through a mediumaccess control (MAC) control element (CE).

Advantageous Effects of Invention

In the disclosure, a change operation from an LTE PDCP to an NR PDCP canbe optimized by embodying a method of minimizing a PDCP re-establishmentoperation, in particular, a loss of data attributable to a PDCP versionchange between LTE and NR in a next-generation mobile communicationsystem.

In the disclosure, a terminal can rapidly perform carrier aggregationactivation when it switches to a connected state because a base stationproperly provides configuration information when the terminal enters aninactive state in a next-generation mobile communication system.

Effects which may be obtained in the disclosure are not limited to theaforementioned effects, and other technical effects not described abovemay be evidently understood by a person having ordinary skill in the artto which the disclosure pertains from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating the architecture of an LTE system towhich reference is made for the description of the disclosure.

FIG. 1B is a diagram illustrating a radio protocol structure in an LTEsystem to which reference is made for the description of the disclosure.

FIG. 1C is a diagram illustrating the architecture of a next-generationmobile communication system to which the disclosure is applied.

FIG. 1D is a diagram illustrating the radio protocol structure of anext-generation mobile communication system to which the disclosure maybe applied.

FIG. 1E is a diagram illustrating a PUSH-based window operation in aPDCP layer in an LTE system.

FIG. 1F is a diagram illustrating the entire PDCP re-establishmentoperation of indicating a change from an LTE PDCP to an NR PDCP, whichis proposed in the disclosure.

FIG. 1G is a diagram illustrating an example of a second PDCPre-establishment pre-operation, which is considered in the disclosure.

FIG. 1H is a diagram illustrating a UE operation performing a PDCPre-establishment operation to which the disclosure is applied.

FIG. 1I is a block diagram illustrating an internal structure of a UE towhich the disclosure has been applied.

FIG. 1J is a block diagram illustrating the configuration of a basestation according to the disclosure.

FIG. 2A is a diagram illustrating the architecture of an LTE system towhich reference is made for the description of the disclosure.

FIG. 2B is a diagram illustrating a radio protocol structure in an LTEsystem to which reference is made for the description of the disclosure.

FIG. 2C is a diagram illustrating the architecture of a next-generationmobile communication system to which the disclosure is applied.

FIG. 2D is a diagram illustrating the radio protocol structure of anext-generation mobile communication system to which the disclosure maybe applied.

FIG. 2E is a diagram describing an operation for carrier aggregationactivation in an LTE system to which reference is made in thedisclosure.

FIG. 2F is a diagram illustrating an operation of performing a carrieraggregation upon transition from an inactive state to a connected state,which is proposed in the disclosure.

FIG. 2G is a diagram describing a given situation in which a secondarycell configuration is maintained in an inactive state, which is proposedin the disclosure.

FIG. 2HA is a diagram illustrating the entire operation of a UE to whichthe disclosure is applied. FIG. 2HB is a diagram illustrating the entireoperation of a UE to which the disclosure is applied.

FIG. 2I is a block diagram illustrating an internal structure of a UE towhich the disclosure has been applied.

FIG. 2J is a block diagram illustrating the configuration of a basestation according to the disclosure.

DETAILED DESCRIPTION

Hereinafter, an operation principle of the disclosure is described indetail with reference to the accompanying drawings. In describing thedisclosure, a detailed description of a related known function orconfiguration will be omitted if it is deemed to make the gist of thedisclosure unnecessarily vague. Furthermore, terms to be describedhereunder have been defined by taking into consideration functions inthe disclosure, and may be different depending on a user, an operator'sintention or practice. Accordingly, each term should be defined based oncontents over the entire specification.

Hereinafter, in the disclosure, terms and names defined in 3rdgeneration partnership project long term evolution (3GPP LTE) standardsor terms and names modified based on the 3GPP LTE standards are used,for convenience of description. However, the disclosure is notrestricted by the terms and names, and may be identically applied tosystems complying with other standards.

Embodiment 1

FIG. 1A is a diagram illustrating the architecture of an LTE system towhich reference is made for the description of the disclosure.

Referring to FIG. 1A, as illustrated, the radio access network of theLTE system includes next-generation evolved Node Bs (hereinafterreferred to as “eNBs”, “Node Bs” or “base stations”) 1 a-05, 1 a-10, 1a-15, and 1 a-20, a mobility management entity (MME) 1 a-25, and aserving-gateway (S-GW) 1 a-30. A user equipment (hereinafter referred toas a “UE” or “terminal”) 1 a-35 accesses an external network through theeNBs 1 a-05˜1 a-20 and the S-GW 1 a-30.

In FIG. 1A, the eNBs 1 a-05˜1 a-20 correspond to the Node Bs of theexisting UMTS system. The eNB is connected to the UE 1 a-35 through aradio channel and performs a more complex function than the existingNode B. In the LTE system, all of types of user traffic including areal-time service, such as voice over IP (VoIP), through the Internetprotocol, are served through a shared channel. Accordingly, a devicethat performs schedules by collecting state information, such as thebuffer state, available transmission power state, and channel state ofUEs, is necessary. The eNBs 1 a-05˜1 a-20 are in charge of such adevice. In general, one eNB controls multiple cells. For example, inorder to implement the transfer rate of 100 Mbps, the LTE system usesorthogonal frequency division multiplexing (hereinafter referred to as“OFDM”) as a radio access technology in the 20 MHz bandwidth, forexample. Furthermore, the LTE system adopts an adaptive modulation &coding (hereinafter referred to as “AMC”) scheme for determining amodulation scheme and a channel coding rate based on the channel stateof a UE. The S-GW 1 a-30 provides a data bearer and generates or removesa data bearer under the control of the MME 1 a-25. The MME is in chargeof various control functions in addition to a mobility managementfunction for a UE, and is connected to multiple base stations.

FIG. 1B is a diagram illustrating a radio protocol structure in an LTEsystem to which reference is made for the description of the disclosure.

Referring to FIG. 1B, the radio protocol of the LTE system includespacket data convergence protocols (PDCPs) 1 b-05 and 1 b-40, radio linkcontrol (RLC) 1 b-10 and 1 b-35, and medium access control (MAC) 1 b-15and 1 b-30 in a UE and an eNB, respectively. The PDCPs 1 b-05 and 1 b-40are in charge of an operation, such as IP headercompression/restoration. Major functions of the PDCP 1 b-05, 1 b-40 aresummarized as follows.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transfer function (Transfer of user data)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs at PDCP re-establishment procedure for RLC AM)    -   Sequence reordering function (For split bearers in DC (only        support for RLC AM): PDCP PDU routing for transmission and PDCP        PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs at PDCP re-establishment procedure for RLC AM)    -   Retransmission function (Retransmission of PDCP SDUs at handover        and, for split bearers in DC, of PDCP PDUs at PDCP data-recovery        procedure, for RLC AM)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU deletion function (Timer-based SDU discard in        uplink.)

The RLC 1 b-10, 1 b-35 reconfigures a PDCP packet data unit (PDU) in aproper size and performs an ARQ operation. Major functions of the RLCare summarized as follows.

-   -   Data transfer function (Transfer of upper layer PDUs)    -   ARQ function (Error Correction through ARQ (only for AM data        transfer))    -   Concatenation, segmentation and reassembly function        (Concatenation, segmentation and reassembly of RLC SDUs (only        for UM and AM data transfer))    -   Re-segmentation function (Re-segmentation of RLC data PDUs (only        for AM data transfer))    -   Sequence reordering function (Reordering of RLC data PDUs (only        for UM and AM data transfer)    -   Duplicate detection function (Duplicate detection (only for UM        and AM data transfer))    -   Error detection function (Protocol error detection (only for AM        data transfer))    -   RLC SDU discard function (RLC SDU discard (only for UM and AM        data transfer))    -   RLC re-establishment function (RLC re-establishment)

The MAC 1 b-15, 1 b-30 is connected to multiple RLC layer devicesconfigured in one UE, and performs an operation of multiplexing RLC PDUswith a MAC PDU and demultiplexing RLC PDUs from a MAC PDU. Majorfunctions of the MAC are summarized as follows.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Priority handling function between logical channels (Priority        handling between logical channels of one UE)    -   Priority handling function between UEs (Priority handling        between UEs by means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

A physical layer (PHY) 1 b-20, 1 b-25 performs an operation ofchannel-coding and modulating higher layer data, generating the higherlayer data into an OFDM symbol, and transmitting the OFDM symbol througha radio channel or demodulating an OFDM symbol received through a radiochannel, channel-decoding the OFDM symbol, and transmitting the OPDMsymbol to a higher layer.

FIG. 1C is a diagram illustrating the architecture of a next-generationmobile communication system to which the disclosure is applied.

Referring to FIG. 1C, the radio access network of a next-generationmobile communication system is configured with a new radio Node B(hereinafter referred to as an “NR NB” or “NR gNB”) 1 c-10 and a newradio core network (NR CN) 1 c-05. A new radio user equipment(hereinafter referred to as an “NR UE” or a “terminal”) 1 c-15 accessesan external network through the NR gNB 1 c-10 and the NR CN 1 c-05.

In FIG. 1C, the NR gNB 1 c-10 corresponds to an evolved Node B (eNB) inthe existing LTE system. The NR gNB is connected to the NR UE 1 c-15through a radio channel, and may provide an excellent service comparedto the existing Node B. A next-generation mobile communication systemrequires a device for performing scheduling by collecting stateinformation, such as the buffer state, available transmission powerstate, and channel state of UEs, because all of types of user trafficare served through a shared channel. The NR gNB 1 c-10 is in charge ofthe device. In general, one NR gNB controls multiple cells. In order toimplement ultra-high speed data transfer compared to the existing LTE,the next-generation mobile communication system may have the existingmaximum bandwidth or more, and the beamforming technology may beadditionally grafted using orthogonal frequency division multiplexing(hereinafter referred to as “OFDM”) as a radio access technology.Furthermore, the next-generation mobile communication system adopts anadaptive modulation & coding (hereinafter referred to as “AMC”) schemeof determining a modulation scheme and channel coding rate based on thechannel state of a UE. The NR CN 1 c-05 performs functions, such asmobility support, a bearer setup, and a QoS configuration. The NR CN 1c-05 is in charge of various control functions in addition to a mobilitymanagement function for a UE, and is connected to multiple basestations. Furthermore, the next-generation mobile communication systemmay also operate in conjunction with the existing LTE system. The NR CNis connected to an MME 1 c-25 through a network interface. The MME isconnected to an eNB 1 c-30, that is, the existing base station.

Hereinafter, an LTE system may be called a first system, and anext-generation mobile communication system may be called a secondsystem.

FIG. 1D is a diagram illustrating the radio protocol structure of anext-generation mobile communication system to which the disclosure maybe applied.

Referring to FIG. 1D, the radio protocol of the next-generation mobilecommunication system is configured with NR PDCPs 1 d-05 and 1 d-40, NRRLC 1 d-10 and 1 d-35, and NR MAC 1 d-15 and 1 d-30 in a UE and an NRbase station, respectively. Major functions of the NR PDCP 1 d-05, 1d-40 may include some of the following functions.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transfer function (Transfer of user data)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs)    -   Sequence reordering function (PDCP PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs)    -   Retransmission function (Retransmission of PDCP SDUs)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU deletion function (Timer-based SDU discard in        uplink.)

In the above description, the reordering function (reordering) of an NRPDCP entity refers to a function of sequentially reordering PDCP PDUs,received from a lower layer, based on a PDCP sequence number (SN), mayinclude a function of delivering data to a higher layer in a reorderedsequence, may include a function of recording lost PDCP PDUs byreordering the sequence, may include a function of making a statusreport on lost PDCP PDUs to the transmission side, and may include afunction of requesting the retransmission of lost PDCP PDUs.

Major functions of the NR RLC 1 d-10, 1 d-35 may include some of thefollowing functions.

-   -   Data transfer function (Transfer of upper layer PDUs)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs)    -   Out-of-sequence delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   ARQ function (Error Correction through ARQ)    -   Concatenation, segmentation and reassembly function        (Concatenation, segmentation and reassembly of RLC SDUs)    -   Re-segmentation function (Re-segmentation of RLC data PDUs)    -   Sequence reordering function (Reordering of RLC data PDUs)    -   Duplicate detection function (Duplicate detection)    -   Error detection function (Protocol error detection)    -   RLC SDU discard function (RLC SDU discard)    -   RLC re-establishment function (RLC re-establishment)

In the above description, the in-sequence delivery function of an NR RLCentity refers to a function of delivering RLC SDUs, received from alower layer, to a higher layer in sequence, and may include a functionof reassembling multiple RLC SDUs if one RLC SDU has been originallysegmented into the multiple RLC SDUs and received and delivering thereassembled RLC SDU. Furthermore, the NR RLC entity may include afunction of reordering received RLC PDUs based on an RLC sequence number(SN) or a PDCP SN, and may include a function of recording lost RLC PDUsby reordering the sequence. Furthermore, the NR RLC entity may include afunction of making a status report on lost RLC PDUs to the transmissionside, and may include a function of requesting the retransmission oflost RLC PDUs. The NR RLC entity may include a function of delivering,to a higher layer, only RLC SDUs prior to a lost RLC SDU in sequence ifthe lost RLC SDU is present. Furthermore, the NR RLC entity may includea function of delivering, to a higher layer, all RLC SDUs receivedbefore a timer starts in sequence if the timer has expired althoughthere is a lost RLC SDU or may include a function of delivering, to ahigher layer, all RLC SDUs received so far if a given timer has expiredalthough there is a lost RLC SDU. Furthermore, the NR RLC entity mayinclude a function of processing RLC PDUs in the sequence that they arereceived (in order of arrival regardless of a sequence, such as asequence number) and delivering the RLC PDUs to a PDCP entity out ofsequence (i.e., out-of sequence delivery). Furthermore, when a segmentis received, the NR RLC entity may receive segments stored in a bufferor to be subsequently received, may reconfigure the segments into onecomplete RLC PDU, may process the RLC PDU, and may deliver the RLC PDUto a PDCP entity. The NR RLC layer may not include a concatenationfunction. The concatenation function may be performed in the NR MAClayer or may be substituted with the multiplexing function of the NR MAClayer.

In the above description, the out-of-sequence delivery function of theNR RLC entity may refer to a function of directly delivering, to ahigher layer, RLC SDUs received from a lower layer out of sequence.Furthermore, the NR RLC entity may include a function of reassemblingmultiple RLC SDUs if one RLC SDU has been originally segmented into themultiple RLC SDUs and received and delivering the reassembled RLC SDU,and may include a function of storing the RLC SN or PDCP SN of receivedRLC PDUs, reordering their sequence, and recording lost RLC PDUs.

The NR MAC 1 d-15, 1 d-30 may be connected to multiple NR RLC layerdevices configured in one UE. Major functions of the NR MAC may includesome of the following functions.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Priority handling function between logical channels (Priority        handling between logical channels of one UE)    -   Priority handling function between UEs (Priority handling        between UEs by means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

An NR PHY layer 1 d-20, 1 d-25 may perform an operation ofchannel-coding and modulating higher layer data, generating the higherlayer data into an OFDM symbol, and transmitting the OFDM symbol to aradio channel or demodulating an OFDM symbol received through a radiochannel, channel-decoding the OFDM symbol, and transferring the OFDMsymbol to a higher layer.

FIG. 1E is a diagram illustrating a PUSH-based window operation in aPDCP layer in an LTE system.

A method of performing re-ordering in an LTE system operates based on aPUSH-based window. This may have a structure in which the window isadvanced based on a lower edge of the window. The lower edge of thewindow is defined as a PDCP sequence number and a hyper frame number(HFN) or a COUNT value delivered to a higher layer most recently. Thismay be defined as a variable called Last_Submitted_PDCP_RX_SN andRX_HFN. In the above description, the COUNT value is configured with 32bits and may be configured with a combination of a PDCP sequence numberand an HFN. The HFN value is increased by 1 whenever the PDCP sequencenumber increases up to a maximum value and is set to 0 again. As in 1e-05 of FIG. 1E, when a packet is received out of a window, it may beconsidered as an old packet and discarded. However, when a packet isreceived within a window as in 1 e-10, it may be considered as a normalpacket. After whether the packet has been redundantly received ischecked, data processing may be performed in a PDCP layer. Furthermore,a Last_Submitted_PDCP_RX_SN variable value is updated by the PDCPsequence number (or COUNT value) of a packet delivered to a higherlayer, and thus the window is advanced. In the above description, thesize of the window may be set as half the space which may be assigned tothe PDCP sequence number. For example, if the length of a PDCP sequencenumber is 12 bits, the size of a window may be set to 2{circumflex over( )}(12−1). In FIG. 1E, a circle, such as 1 e-05 or 1 e-10, indicates awindow, and a smaller circle within the circle may be used to determinean HFN value. That is, a circle having a different color or pattern maymean that it has a different HFN.

In NR, a stable variable has been reduced compared to LTE. That is,values defined as the existing PDCP sequence number and HN may bedefined as a COUNT-based unified value. For reference, Tx/Rx PDCP statevariables in LTE and NR (Tx PDCP state variables for LTE and NR, Rx PDCPstate variables for LTE and NR) may be the same as those in Table 1 andTable 2.

TABLE 1 LTE NR Next_PDCP_TX_SN Indicate the PDCP SN of a TX_NEXTIndicate the COUNT of a PDCP SDU to be subsequently PDCP SDU to besubsequently transmitted in a PDCP entity transmitted in a PDCP entitySet to 0 upon PDCP An initial value is set to 0 establishment TX_HFNIndicate an HFN value generated from a COUNT value used for PDCP PDUs ina PDCP entity Set to 0 upon PDCP establishment

TABLE 2 LTE NR Next_PDCP_RX_SN Indicate the PDCP SN of a RX_NEXT COUNTvalue of a PDCP PDCP SDU expected to be SDU expected to be subsequentlyreceived in a subsequently received PDCP entity An initial value is setto 0 Set to 0 upon PDCP establishment RX_HFN Indicate an HFN valuegenerated from a COUNT value used for PDCP PDUs received in a PDCPentity Set to 0 upon PDCP establishment Last_Submitted_PDCP_RX_SNApplied only in a PDCP RX_DELIV Indicate the COUNT value entity mappedto a DRB, that of the last PDCP SDU is, RLC AM delivered to a higherlayer Indicate the SN of the last An initial value is set to PDCP SDUdelivered to a 2{circumflex over ( )}32-1 higher layer Set as a maximumPDCP SN value upon PDCP establishment

FIG. 1F is a diagram illustrating the entire PDCP re-establishmentoperation of indicating a change from an LTE PDCP to an NR PDCP, whichis proposed in the disclosure.

In the disclosure, basically, a gNB needs to both LTE and NR. Inparticular, it is assumed that a gNB supports LTE PDCP and NR PCDPfunctions. This is essential for an NR implementation of anon-standalone method based on an EN-DC mode in which LTE and NR operateas dual connectivity (DC). That is, a base station supporting EN-DCneeds to be capable of two versions of PDCP configurations because ithas to support both the LTE and PDCP functions. Basically, PDCPre-establishment is indicated in a change a bearer type. This may beperformed according to a change procedure of handover or a sequencenumber (SN). In the disclosure, the entire PDCP re-establishmentprocedure is handled if a version is changed to an NR PDCP with respectto a DRB×operating as an LTE PDCP.

Referring back to FIG. 1F, at step 1 f-10, a UE 1 f-01 may receiveconfiguration information for a given DRB× from a base station 1 f-02 inan RRC connected state 1 f-05. The DRB configuration includes an initialconfiguration for the corresponding DRB×. The corresponding DRB× may bea tunnel for transmitting and receiving data to and from an LTE UE, andmay include configuration information for a PDCP, RLC and Logicalchannel. At step 1 f-15, the DRB× may be generated and data transmissionand reception may be performed between the UE 1 f-01 and the basestation 1 f-02 depending on the configuration. At step 1 f-20, when anevent, such as handover (HO), occurs while the data transmission andreception are performed through step 1 f-15, the UE 1 f-01 may receive,from the base station 1 f-02, an indication for PDCP re-establishmentthrough an RRC reconfiguration message. The RRC reconfiguration messagecorresponds to a bearer change, and may indicate re-establishment forRLC or a Logical channel or MAC reset. In the disclosure, such a PDCPre-establishment operation in LTE is defined as a first PDCPre-establishment operation. At step 1 f-25, the PDCP of the UE 1 f-01that has received the RRC reconfiguration message may perform a firstPDCP re-establishment operation on the PDCP of a DRB×, such as thatillustrated in Table 3.

TABLE 3 First PDCP re-establishment: normal procedure (applied to a DRBmapped to RLC AM) Uplink (Transmitting entity) Downlink (Receivingentity) Reset header compression Process PDCP PDUs received Apply areceived cipher from a lower layer algorithm and key Reset headercompression Start the retransmission of Stop and reset t-reordering PDCPSDUs (from the Apply the cipher algorithm first PDCP SDU for which andkey the successful delivery of a corresponding PDCP PDU has not beenconfirmed by lower layers); Generate a status report (Use First MissingSequence number)

Furthermore, at step 1 f-30, the UE 1 f-01 may transmit and receive datato and from the base station 1 f-02 through the PDCP configurationapplied through the first PDCP re-establishment procedure. At step 1f-35, the UE 1 f-01 operating as LTE may receive, from the base station1 f-02 supporting NR, an indication for data transmission related to NRthrough handover. That is, transmission through an NR DRB needs to beperformed. In such a case, the UE may receive, from the base station, asecond PDCP re-establishment indication including an NR PDCP settingvalue through an RRC reconfiguration message. For example, the PDCPre-establishment configuration may be a control message to newlyconfigure an NR PDCP-config with respect to the DRB×. In this case, thePDCP re-establishment configuration may also include configurationinformation (SDAP mode information, QoS flow ID configurationinformation, reflective indication configuration information) for anSDAP layer. That is, in LTE, when a PDCH change from LTE to NR isindicated, a configuration for a new SDAP is necessary because an SDAPlayer is not present. When the UE 1 f-01 receives an RRC messageincluding the second PDCP re-establishment indication, at step 1 f-40,it may perform a second PDCP re-establishment pre-operation and a secondPDCP re-establishment operation on the DRB×.

The second PDCP re-establishment pre-operation means an operation ofprocessing all of the 2nd set of PDCP PDUs as PDCP SDUs in the receivingentity of an LTE PDCP. In this case, the 2nd set of PDCP PDUs means aPDCP PDU received due to the re-establishment operation of a lowerlayer. That is, the second PDCP re-establishment pre-operation is thestep of processing LTE PDCP PDUs received prior to a PDCP operationbased on a version change of a PDCP from LTE to NR. The 2nd set of PDCPPDUs is configured with an LTE PDCP format. Accordingly, the aboveoperation is performed in the LTE PDCP in order to correctly interpretinformation of an LTE PDCP header. The second PDCP re-establishmentpre-operation will be described using an example in FIG. 1G.

The second PDCP re-establishment operation means an operation performedin the PDCP of the UE 1 f-01 after an indication for a change from anLTE PDCP to an NR PDCP is received. For example, operations listed inTable 4 may be performed.

TABLE 4 Second PDCP re-establishment: new procedure (applied to a DRBmapped to RLC AM) Uplink (Transmitting entity) Downlink (Receivingentity) Reset header compression Adjust an LTE RX state variable to anApply a received ciphering algorithm and key NR RX state variable(RX_DELIV and Adjust an LTE TX state variable to an NR TX state RX_NEXTof the following NR RX variable (set TX_NEXT using variables areconfigured by the NEXT_PDCP_TX_SN and TX_HFN, that is, concatenation ofvalues configure TX_NEXT by concatenating TX_HFN corresponding to an HFNand an SN in and NEXT_PDCP_TX_SN) LTE) Start a PDCP SDU retransmissionprocedure Set RX_DELIV using If an SDAP entity is configured and aLast_Submited_PDCP_RX_SN and transmission mode is not set (or in thesame meaning RX_HFN if an SDAP header including given information is Setan HFN(RX_DELIV) using inserted) RX_HFN A PDCP delivers a 1^(st) set ofPDCP SDUs to an Set RX_NEXT using SDAP layer in ascending power of acorresponding NEXT_PDCP_RX_SN and RX_HFN COUTN value (in this case, the1^(st) set of PDCP Reset header compression SDUs means PDCP SDUs forwhich the successful Stop and reset t-reordering delivery of a PDCP PDUhas not been confirmed by Apply a received ciphering algorithm a lowerlayer) and key The SDAP attaches an SDAP header to the 1^(st) Initiatet-reordering if a stored PDCP set of PDCP SDUs delivered by the PDCP andthen SDU is present. delivers them to the PDCP again in order of thePDCP SDUs received. After processing all the 1^(st) set of PDCP SDUs,the SDAP attaches an SDAP header to IP packets downloaded from a higherlayer and delivers them to a lower layer. Process the PDCP SDUs receivedfrom the SDAP Start retransmission Generate a status report (using FirstMissing Sequence Number)

FIG. 1G is a diagram illustrating an example of a second PDCPre-establishment pre-operation, which is considered in the disclosure.

As the second PDCP re-establishment pre-operation has been described inFIG. 1F, the second PDCP re-establishment pre-operation means anoperation of processing all of a 2nd set of PDCP PDUs into PDCP SDUs inthe receiving entity of an LTE PDCP. In this case, the 2nd set of PDCPPDUs means PDCP PDUs received due to the re-establishment operation of alower layer. That is, the second PDCP re-establishment pre-operation isthe step of processing LTE PDCP PDUs received prior to a PDCP operationbased on a version change of a PDCP from LTE to NR. In order tocorrectly interpret information of an LTE PDCP header, the aboveoperation is performed in an LTE PDCP because the 2nd set of PDCP PDUsis configured with an LTE PDCP format.

In FIG. 1G, if a UE 1 g-25˜1 g-40 receives a PDCP the packet from a basestation 1 g-05˜1 g-20 that transmits LTE PDCP data and receives anindication for a version change in an NR PDCP through a bearerreconfiguration, for a given cause, for example, through handover, apre-operation is necessary so that an SDAP does not need to distinguishbetween a packet to which an SDAP header has been attached (one newlyreceived in the NR PDCP) and a packet to which an SDAP header has notbeen attached (one that had been received in the LTE PDCP). This isdescribed based on the example illustrated in the figure. A case wherethe base station has transmitted PDCP PDUs whose PDCP SNs are 0, 1, 2,3, 4, 5, 6, and 7 to the UE and the UE has not received acknowledgementfor PDCP PDUs whose PDCP SNs are 4 and 5 from a lower layer.

-   -   1. A non transparent SDAP configuration (i.e., if SDAP header        contents are present):

An out-of-sequence PDCP SDUs (corresponding to PDCP PDUs whose PDCP SNsare 6 and 7) are immediately delivered to an upper layer so that they donot experience an SDAP. This means that PDCP SNs whose reception has notbeen completed do not process PDCP SDUs 4 and 5. That is, the losslessof a PDCP packet is not applied.

-   -   2. A transparent SDAP configuration (or if an SDAP header has        not been configured):

A UE stores out-of-sequence PDCP SDUs (corresponding to PDCP PDUs whosePDCP SNs are 6 and 7) in a buffer. Thereafter, if PDCP PDUs whose PDCPSNs are 4 and 5 are received from a changed NR PDCP, the UE delivers thePDCP PDUs to an upper layer in sequence.

As described above, the second PDCP re-establishment pre-operation is anoperation of enabling an SDAP to not need to distinguish between apacket to which an SDAP header has been attached (one newly received inthe NR PDCP) and a packet to which an SDAP header has not been attached(one that had been received in the LTE PDCP) in a DRB received from thebase station after the second PDCP re-establishment operation isreceived.

FIG. 1H is a diagram illustrating a UE operation performing a PDCPre-establishment operation to which the disclosure is applied.

A UE whose RRC connection with a base station has been configured atstep 1 h-05 may identify the DRB configuration of an RRC reconfigurationmessage received from the base station when an event in which handoveror an SN change procedure is triggered occurs at step 1 h-10. At step 1h-15, the UE may identify whether a PDCP re-establishment configurationis included in the corresponding DRB configuration. Furthermore, if afirst condition is satisfied, at step 1 h-20, the UE performs a firstPDCP re-establishment operation. In the above description, the firstcondition corresponds to a case where the UE has received an LTE PDCPconfiguration from the base station, and a detailed operation thereofwill be described in FIG. 1F. In contrast, if a PDCP re-establishmentconfiguration is included in the corresponding DRB configuration and asecond condition is satisfied, at step 1 h-25, the UE performs a secondPDCP re-establishment pre-operation. Thereafter, at step 1 h-30, the UEperforms a second PDCP re-establishment operation. In the abovedescription, the second condition corresponds to a case where the UEoperates based on an LTE PDCP configuration and receives an indicationfor an NR PDCP configuration from the base station, and a detailedoperation thereof will be described in FIGS. 1F and 1G.

FIG. 1I is a block diagram illustrating an internal structure of a UE towhich the disclosure has been applied.

Referring to the figure, the UE includes a radio frequency (RF)processor 1 i-10, a baseband processor 1 i-20, a memory 1 i-30, and acontroller 1 i-40.

The RF processor 1 i-10 performs a function for transmitting andreceiving signals through a radio channel, such as the band conversion,amplification, etc. of a signal. That is, the RF processor 1 i-10up-converts a baseband signal received from the baseband processor 1i-20 into an RF band signal, transmits the RF band signal through anantenna, and down-converts an RF band signal received through theantenna into a baseband signal. For example, the RF processor 1 i-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital to analog convertor (DAC), and an analogto digital convertor (ADC). In FIG. 1I, only one antenna has beenillustrated, but the UE may include multiple antennas. Furthermore, theRF processor 1 i-10 may include multiple RF chains. Furthermore, the RFprocessor 1 i-10 may perform beamforming. For the beamforming, the RFprocessor 1 i-10 may adjust the phase and size of each of signalstransmitted/received through multiple antennas or antenna elements.Furthermore, the RF processor may perform MIMO. When the RF processorperforms the MIMO operation, it may receive multiple layers.

The baseband processor 1 i-20 performs a baseband signal and inter-bitstream conversion function based on the physical layer standard of asystem. For example, when data is transmitted, the baseband processor 1i-20 generates complex symbols by coding and modulating a transmissionbit stream. Furthermore, when data is received, the baseband processor 1i-20 reconstructs a reception bit stream from a baseband signal receivedfrom the RF processor 1 i-10 through demodulation and decoding. Forexample, if an orthogonal frequency division multiplexing (OFDM) schemeis applied, when data is transmitted, the baseband processor 1 i-20generates complex symbols by coding and modulating a transmission bitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols through an inverse fast Fourier transform (IFFT) operationand cyclic prefix (CP) insertion. Furthermore, when data is received,the baseband processor 1 i-20 segments a baseband signal received fromthe RF processor 1 i-10 in an OFDM symbol unit, reconstructs signalsmapped to subcarriers through a fast Fourier transform (FFT) operation,and reconstructs a reception bit stream through demodulation anddecoding.

The baseband processor 1 i-20 and the RF processor 1 i-10 transmit andreceive signals as described above. Accordingly, the baseband processor1 i-20 and the RF processor 1 i-10 may be called a transmitter, areceiver, a transceiver or a communication unit. Furthermore, at leastone of the baseband processor 1 i-20 and the RF processor 1 i-10 mayinclude multiple communication modules in order to support differentmultiple radio access technologies. Furthermore, at least one of thebaseband processor 1 i-20 and the RF processor 1 i-10 may includedifferent communication modules in order to process signals of differentfrequency bands. For example, the different radio access technologiesmay include a wireless LAN (e.g., IEEE 802.11), a cellular network(e.g., LTE), etc. Furthermore, the different frequency bands may includea super high frequency (SHF) (e.g., 2 NRHz, NRhz) band and a millimeterwave (e.g., 60 GHz) band.

The memory 1 i-30 stores data, such as a basic program, an applicationprogram, and configuration information for the operation of the UE. Inparticular, the memory 1 i-30 may store information related to a secondaccess node that performs wireless communication using a second radioaccess technology. The memory 1 i-30 provides stored data in response toa request from the controller 1 i-40.

The controller 1 i-40 controls an overall operation of the UE. Forexample, the controller 1 i-40 transmits/receives a signal through thebaseband processor 1 i-20 and the RF processor 1 i-10. Furthermore, thecontroller 1 i-40 writes data in the memory 1 i-40 and reads data fromthe memory 1 i-40. To this end, the controller 1 i-40 may include atleast one processor. For example, the controller 1 i-40 may include acommunication processor (CP) performing control for communication and anapplication processor (AP) controlling a higher layer, such as anapplication program.

FIG. 1J is a block diagram illustrating the configuration of a basestation according to the disclosure.

As illustrated in the figure, the base station is configured to includean RF processor 1 j-10, a baseband processor 1 j-20, a backhaulcommunication unit 1 j-30, a memory 1 j-40 and a controller 1 j-50.

The RF processor 1 j-10 performs a function for transmitting andreceiving signals through a radio channel, such as the band conversionand amplification of a signal. That is, the RF processor 1 j-10up-converts a baseband signal received from the baseband processor 1j-20 into an RF band signal, transmits the RF band signal through anantenna, and down-converts an RF band signal received through theantenna into a baseband signal. For example, the RF processor 1 j-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a DAC, and an ADC. In FIG. 1K, only one antennahas been illustrated, but the first access node may include multipleantennas. Furthermore, the RF processor 1 j-10 may include multiple RFchains. Furthermore, the RF processor 1 j-10 may perform beamforming.For the beamforming, the RF processor 1 j-10 may adjust the phase andsize of each of signals transmitted/received multiple antennas orantenna elements. The RF processor may perform a downlink MIMO operationby transmitting one or more layers.

The baseband processor 1 j-20 performs a baseband signal and inter-bitstream conversion function based on the physical layer standard of afirst radio access technology. For example, when data is transmitted,the baseband processor 1 j-20 generates complex symbols by coding andmodulating a transmission bit stream. Furthermore, when data isreceived, the baseband processor 1 j-20 reconstructs a reception bitstream from a baseband signal received from the RF processor 1 j-10through demodulation and decoding. For example, if the OFDM scheme isapplied, when data is transmitted, the baseband processor 1 j-20generates complex symbols by coding and modulating a transmission bitstream, maps the complex symbols to subcarriers, and configures OFDMsymbols through IFFT operation and CP insertion. Furthermore, when datais received, the baseband processor 1 j-20 segments a baseband signalreceived from the RF processor 1 j-10 in an OFDM symbol unit,reconstructs signals mapped to subcarriers through FFT operation, andthen reconstructs a reception bit stream through demodulation anddecoding. The baseband processor 1 j-20 and the RF processor 1 j-10transmit and receive signals as described above. Accordingly, thebaseband processor 1 j-20 and the RF processor 1 j-10 may be called atransmitter, a receiver, a transceiver, a communication unit or awireless communication unit.

The backhaul communication unit 1 j-30 provides an interface forperforming communication with other nodes within a network. That is, thebackhaul communication unit 1 j-30 physically converts a bit stream,transmitted from a primary base station to another node, for example, asecondary base station, a core network, etc., into a physical signal,and converts a physical signal, received from another node, into a bitstream.

The memory 1 j-40 stores data, such as a basic program, an applicationprogram, and configuration information for the operation of the basestation. Specifically, the memory 1 j-40 may store information on abearer allocated to an accessed UE and measurement results reported byan accessed UE. Furthermore, the memory 1 j-40 may store information,that is, a criterion by which whether to provide a UE with multipleconnections is determined. Furthermore, the memory 1 j-40 providesstored data in response to a request from the controller 1 j-50.

The controller 1 j-50 controls an overall operation of the primary basestation. For example, the controller 1 j-50 transmits/receives a signalthrough the baseband processor 1 j-20 and the RF processor 1 j-10 orthrough the backhaul communication unit 1 j-30. Furthermore, thecontroller 1 j-50 writes data in the memory 1 j-40 and reads data fromthe memory 1 j-40. To this end, the controller 1 j-50 may include atleast one processor.

The following is the summarized contents of contents described in thedisclosure.

The disclosure is for defining a PDCP re-establishment operation from anLTE PDCP to an NR PDCP.

Furthermore, the entire operation according to an embodiment of thedisclosure may be as follows.

-   -   1. A UE establishes an RRC connection in LTE    -   2. Receives a control message indicating a DRB×configuration:        LTE PDCP-config, LTE RLC-config, etc.    -   3. Data transmission and reception in the DRB×    -   4. Receive a control message indicative of first        re-establishment execution for the PDCP of the DRB×(e.g., a        control message indicating handover)    -   5. First re-establishment execution for the PDCP of the DRB×

DRB mapped on RLC AM (First PDCP re-establishment; normal procedure)Uplink (Transmitting entity) Downlink (Receiving entity) Reset headercompression; Process the PDCP PDUs received Apply the cipher algorithmand key; from lower layer Start retransmission of PDCP SDUs Reset headercompression (from the first PDCP SDU for Stop and reset t-reorderingwhich the successful delivery of the Apply the cipher algorithm and keycorresponding PDCP PDU has not been confirmed by lower layers); Compilea status report; Use First Missing Sequence number

-   -   6. Data transmission and reception in the DRB×    -   7. Receive a control message indicating second re-establishment        execution for the PDCP of the DRB×(e.g., a control message to        newly configure NR PDCP-config for the DRB×). The message may        also include SDAP configuration information.    -   8. Second re-establishment pre-operation and second        reestablishment operation execution for the DRB×        -   Pre-operation (execution only in the receiving entity)

An LTE PDCP receiving entity may process all of a 2nd set of PDCP PDUsinto PDCP SDUs (the 2nd set of PDCP PDUs may mean PDCP PDUs received dueto the re-establishment operation of a lower layer).->the aboveoperation is performed in an LTE PDCP in order to correctly interpretinformation of an LTE PDCP header.

Out-of-sequence PDCP SDUs are immediately delivered to an upper layerwithout passing through an SDAP if a non transparent SDAP is to beconfigured (lossless is not applied). Furthermore, if a transparent SDAPis to be applied, out-of-sequence PDCP SDUs are stored in abuffer.->this is for enabling an SDAP to need not to distinguish apacket to which an SDAP header has been attached (one newly received inthe NR PDCP) and a packet to which an SDAP header has not been attached(one that had been received in the LTE PDCP).

-   -   Second re-establishment operation

DRB mapped on RLC AM (Second PDCP re-establishment, new procedure)Uplink (Transmitting entity) Downlink (Receiving entity) Reset headercompression Set RX_DELIV using Apply the ciphering algorithm and keyLast_Submited_PDCP_RX_SN and Set TX_NEXT using NEXT_PDCP_TX_SN andRX_HFN TX_HFN (adjust an LTE TX state variable to an NR SetHFN(RX_DELIV) using RX_HFN TX state variable) Set RX_NEXT using Startthe retransmission of PDCP SDUs NEXT_PDCP_RX_SN and RX_HFN If an SDAPentity is configured and it is not a Reset header compressiontransmission mode Stop and reset t-reordering PDCP forwards a 1^(st) setof PDCP SDUs to the Initiate t-reordering if a stored PDCP SDAP in theascending order of the associated SDU is present COUTN (the 1^(st) setof PDCP SDUs are PDCP SDUs Apply the ciphering algorithm and key forwhich the successful delivery of a PDCP PDU has not been confirmed by alower layer) The SDAP attaches an SDAP header to the 1^(st) set of PDCPSDUs delivered by the PDCP and then delivers them to the PDCP again inorder of the PDCP SDUs received. After processing all the 1^(st) set ofPDCP SDUs, the SDAP attaches an SDAP header to IP packets downloadedfrom a higher layer and delivers them to a lower layer. Process the PDCPSDUs received from the SDAP Start retransmission Compile a status reportusing First Missing Count

-   -   9. Data transmission and reception in the DRB×

Embodiment 2

FIG. 2A is a diagram illustrating the architecture of an LTE system towhich reference is made for the description of the disclosure.

Referring to FIG. 2A, as illustrated, the radio access network of theLTE system includes next-generation evolved Node Bs (hereinafterreferred to as “eNBs”, “Node Bs” or “base stations”) 2 a-05, 2 a-10, 2a-15, and 2 a-20, a mobility management entity (MME) 2 a-25, and aserving-gateway (S-GW) 2 a-30. A user equipment (hereinafter referred toas a “UE” or “terminal”) 2 a-35 accesses an external network through theeNBs 2 a-05˜2 a-20 and the S-GW 2 a-30.

In FIG. 2A, the eNBs 2 a-05˜2 a-20 correspond to the Node Bs of theexisting UMTS system. The eNB is connected to the UE 2 a-35 through aradio channel and performs a more complex function than the existingNode B. In the LTE system, all of types of user traffic including areal-time service, such as voice over IP (VoIP), through the Internetprotocol, are served through a shared channel. Accordingly, a devicethat performs schedules by collecting state information, such as thebuffer state, available transmission power state, and channel state ofUEs, is necessary. The eNBs 2 a-05˜2 a-20 are in charge of such adevice. In general, one eNB controls multiple cells. For example, inorder to implement the transfer rate of 100 Mbps, the LTE system usesorthogonal frequency division multiplexing (hereinafter referred to as“OFDM”) as a radio access technology in the 20 MHz bandwidth, forexample. Furthermore, the LTE system adopts an adaptive modulation &coding (hereinafter referred to as “AMC”) scheme for determining amodulation scheme and a channel coding rate based on the channel stateof a UE. The S-GW 2 a-30 provides a data bearer and generates or removesa data bearer under the control of the MME 2 a-25. The MME is in chargeof various control functions in addition to a mobility managementfunction for a UE, and is connected to multiple base stations.

FIG. 2B is a diagram illustrating a radio protocol structure in an LTEsystem to which reference is made for the description of the disclosure.

Referring to FIG. 2B, the radio protocol of the LTE system includespacket data convergence protocols (PDCPs) 2 b-05 and 2 b-40, radio linkcontrol (RLC) 2 b-10 and 2 b-35, and medium access control (MAC) 2 b-15and 2 b-30 in a UE and an eNB, respectively. The PDCPs 2 b-05 and 2 b-40are in charge of an operation, such as IP headercompression/restoration. Major functions of the PDCP 2 b-05, 2 b-40 aresummarized as follows.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transfer function (Transfer of user data)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs at PDCP re-establishment procedure for RLC AM)    -   Sequence reordering function (For split bearers in DC (only        support for RLC AM): PDCP PDU routing for transmission and PDCP        PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs at PDCP re-establishment procedure for RLC AM)    -   Retransmission function (Retransmission of PDCP SDUs at handover        and, for split bearers in DC, of PDCP PDUs at PDCP data-recovery        procedure, for RLC AM)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU deletion function (Timer-based SDU discard in        uplink.)

The RLC 2 b-10, 2 b-35 reconfigures a PDCP packet data unit (PDU) in aproper size and performs an ARQ operation. Major functions of the RLCare summarized as follows.

-   -   Data transfer function (Transfer of upper layer PDUs)    -   ARQ function (Error Correction through ARQ (only for AM data        transfer))    -   Concatenation, segmentation and reassembly function        (Concatenation, segmentation and reassembly of RLC SDUs (only        for UM and AM data transfer))    -   Re-segmentation function (Re-segmentation of RLC data PDUs (only        for AM data transfer))    -   Sequence reordering function (Reordering of RLC data PDUs (only        for UM and AM data transfer)    -   Duplicate detection function (Duplicate detection (only for UM        and AM data transfer))    -   Error detection function (Protocol error detection (only for AM        data transfer))    -   RLC SDU discard function (RLC SDU discard (only for UM and AM        data transfer))    -   RLC re-establishment function (RLC re-establishment)

The MAC 2 b-15, 2 b-30 is connected to multiple RLC layer devicesconfigured in one UE, and performs an operation of multiplexing RLC PDUswith a MAC PDU and demultiplexing RLC PDUs from a MAC PDU. Majorfunctions of the MAC are summarized as follows.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Priority handling function between logical channels (Priority        handling between logical channels of one UE)    -   Priority handling function between UEs (Priority handling        between UEs by means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

A physical layer (PHY) 2 b-20, 2 b-25 performs an operation ofchannel-coding and modulating higher layer data, generating the higherlayer data into an OFDM symbol, and transmitting the OFDM symbol througha radio channel or demodulating an OFDM symbol received through a radiochannel, channel-decoding the OFDM symbol, and transmitting the OPDMsymbol to a higher layer.

FIG. 2C is a diagram illustrating the architecture of a next-generationmobile communication system to which the disclosure is applied.

Referring to FIG. 2C, the radio access network of a next-generationmobile communication system is configured with a new radio Node B(hereinafter referred to as an “NR NB” or “NR gNB”) 2 c-10 and a newradio core network (NR CN) 2 c-05. A new radio user equipment(hereinafter referred to as an “NR UE” or a “terminal”) 2 c-15 accessesan external network through the NR gNB 2 c-10 and the NR CN 2 c-05.

In FIG. 2C, the NR gNB 2 c-10 corresponds to an evolved Node B (eNB) inthe existing LTE system. The NR gNB is connected to the NR UE 2 c-15through a radio channel, and may provide an excellent service comparedto the existing Node B. A next-generation mobile communication systemrequires a device for performing scheduling by collecting stateinformation, such as the buffer state, available transmission powerstate, and channel state of UEs, because all of types of user trafficare served through a shared channel. The NR gNB 2 c-10 is in charge ofthe device. In general, one NR gNB controls multiple cells. In order toimplement ultra-high speed data transfer compared to the existing LTE,the next-generation mobile communication system may have the existingmaximum bandwidth or more, and the beamforming technology may beadditionally grafted using orthogonal frequency division multiplexing(hereinafter referred to as “OFDM”) as a radio access technology.Furthermore, the next-generation mobile communication system adopts anadaptive modulation & coding (hereinafter referred to as “AMC”) schemeof determining a modulation scheme and channel coding rate based on thechannel state of a UE. The NR CN 2 c-05 performs functions, such asmobility support, a bearer setup, and a QoS configuration. The NR CN 2c-05 is in charge of various control functions in addition to a mobilitymanagement function for a UE, and is connected to multiple basestations. Furthermore, the next-generation mobile communication systemmay also operate in conjunction with the existing LTE system. The NR CNis connected to an MME 2 c-25 through a network interface. The MME isconnected to an eNB 2 c-30, that is, the existing base station.

FIG. 2D is a diagram illustrating the radio protocol structure of anext-generation mobile communication system to which the disclosure maybe applied.

Referring to FIG. 2D, the radio protocol of the next-generation mobilecommunication system is configured with NR PDCPs 2 d-05 and 2 d-40, NRRLC 2 d-10 and 2 d-35, and NR MAC 2 d-15 and 2 d-30 in a UE and an NRbase station, respectively. Major functions of the NR PDCP 2 d-05, 2d-40 may include some of the following functions.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transfer function (Transfer of user data)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs)    -   Sequence reordering function (PDCP PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs)    -   Retransmission function (Retransmission of PDCP SDUs)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU deletion function (Timer-based SDU discard in        uplink.)

In the above description, the reordering function (reordering) of an NRPDCP entity refers to a function of sequentially reordering PDCP PDUs,received from a lower layer, based on a PDCP sequence number (SN), mayinclude a function of delivering data to a higher layer in a reorderedsequence, may include a function of recording lost PDCP PDUs byreordering the sequence, may include a function of making a statusreport on lost PDCP PDUs to the transmission side, and may include afunction of requesting the retransmission of lost PDCP PDUs.

Major functions of the NR RLC 2 d-10, 2 d-35 may include some of thefollowing functions.

-   -   Data transfer function (Transfer of upper layer PDUs)    -   In-sequence delivery function (In-sequence delivery of upper        layer PDUs)    -   Out-of-sequence delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   ARQ function (Error Correction through ARQ)    -   Concatenation, segmentation and reassembly function        (Concatenation, segmentation and reassembly of RLC SDUs)    -   Re-segmentation function (Re-segmentation of RLC data PDUs)    -   Sequence reordering function (Reordering of RLC data PDUs)    -   Duplicate detection function (Duplicate detection)    -   Error detection function (Protocol error detection)    -   RLC SDU discard function (RLC SDU discard)    -   RLC re-establishment function (RLC re-establishment)

In the above description, the in-sequence delivery function of an NR RLCentity refers to a function of delivering RLC SDUs, received from alower layer, to a higher layer in sequence, and may include a functionof reassembling multiple RLC SDUs if one RLC SDU has been originallysegmented into the multiple RLC SDUs and received and delivering thereassembled RLC SDU. Furthermore, the NR RLC entity may include afunction of reordering received RLC PDUs based on an RLC sequence number(SN) or a PDCP SN, and may include a function of recording lost RLC PDUsby reordering the sequence. Furthermore, the NR RLC entity may include afunction of making a status report on lost RLC PDUs to the transmissionside, and may include a function of requesting the retransmission oflost RLC PDUs. The NR RLC entity may include a function of delivering,to a higher layer, only RLC SDUs prior to a lost RLC SDU in sequence ifthe lost RLC SDU is present. Furthermore, the NR RLC entity may includea function of delivering, to a higher layer, all RLC SDUs receivedbefore a timer starts in sequence if the timer has expired althoughthere is a lost RLC SDU or may include a function of delivering, to ahigher layer, all RLC SDUs received so far if a given timer has expiredalthough there is a lost RLC SDU. Furthermore, the NR RLC entity mayinclude a function of processing RLC PDUs in the sequence that they arereceived (in order of arrival regardless of a sequence, such as asequence number) and delivering the RLC PDUs to a PDCP entity out ofsequence (i.e., out-of sequence delivery). Furthermore, when a segmentis received, the NR RLC entity may receive segments stored in a bufferor to be subsequently received, may reconfigure the segments into onecomplete RLC PDU, may process the RLC PDU, and may deliver the RLC PDUto a PDCP entity. The NR RLC layer may not include a concatenationfunction. The concatenation function may be performed in the NR MAClayer or may be substituted with the multiplexing function of the NR MAClayer.

In the above description, the out-of-sequence delivery function of theNR RLC entity may refer to a function of directly delivering, to ahigher layer, RLC SDUs received from a lower layer out of sequence.Furthermore, the NR RLC entity may include a function of reassemblingmultiple RLC SDUs if one RLC SDU has been originally segmented into themultiple RLC SDUs and received and delivering the reassembled RLC SDU,and may include a function of storing the RLC SN or PDCP SN of receivedRLC PDUs, reordering their sequence, and recording lost RLC PDUs.

The NR MAC 2 d-15, 2 d-30 may be connected to multiple NR RLC layerdevices configured in one UE. Major functions of the NR MAC may includesome of the following functions.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Priority handling function between logical channels (Priority        handling between logical channels of one UE)    -   Priority handling function between UEs (Priority handling        between UEs by means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

An NR PHY layer 2 d-20, 2 d-25 may perform an operation ofchannel-coding and modulating higher layer data, generating the higherlayer data into an OFDM symbol, and transmitting the OFDM symbol to aradio channel or demodulating an OFDM symbol received through a radiochannel, channel-decoding the OFDM symbol, and transferring the OFDMsymbol to a higher layer.

The disclosure proposes methods for a UE to perform carrier aggregationactivation without a delay when the UE makes transition from an inactivestate to a connected state in a next-generation mobile communicationsystem.

In a network viewpoint, if a UE wants to activate and deactivate acarrier aggregation for the corresponding UE as fast as possible, butthe UE makes transition from an inactive state to a connected state, itmay be configured based on an operation when making transition from aprevious idle state to a connected state. However, in such a case, theUE has to perform all processes of newly reconfiguring a carrieraggregation. This acts as limits to an object of activating a fastcarrier aggregation. First, an operation process in an LTE system isdescribed, and a solution is proposed.

FIG. 2E is a diagram describing an operation for carrier aggregationactivation in an LTE system to which reference is made in thedisclosure.

Referring to FIG. 2 e , if downlink data is present, at step 2 e-05, aUE 2 e-01 may receive paging from a base station 2 e-02. Furthermore, atstep 2 e-10 to step 2 e-20, the UE 2 e-01 may perform a step forestablishing an RRC connection. That is, at step 2 e-10, the UE 2 e-01may transmit an RRC connection request message to the base station 2e-02. At step 2 e-15, the UE 2 e-01 may receive an RRC connection setupmessage from the base station 2 e-02. Furthermore, at step 2 e-20, theUE 2 e-01 may transmit an RRC connection setup complete message to thebase station 2 e-02. The step of receiving paging (step 2 e-05) may beomitted if data from the UE 2 e-01 occurs. At step 2 e-25, the UE 2 e-01makes transition to an RRC connected state through steps 2 e-05 to 2e-20. Thereafter, the base station 2 e-02 may receive a UE capabilityfrom the UE 2 e-01, and may determine whether to configure secondarycells for a carrier aggregation in the corresponding UE. At steps 2 e-30and 2 e-35, the base station 2 e-02 may indicate a secondary cellconfiguration for a carrier aggregation in the UE 2 e-01 through an RRCreconfiguration procedure (the transmission and reception of an RRCconnection reconfiguration message and an RRC connection reconfigurationcomplete message). Thereafter, at step 2 e-40, the base station 2 e-02may determine actually necessary timing among the configured secondarycells, and may transmit, to the UE 2 e-01, an MAC CE indicating theactivation of a carrier aggregation.

In a current LTE system, a time delay occurs in activating a carrieraggregation for secondary cells (SCells). In this case, secondary cellsare not optimized and configured because a primary serving celltransmits all data before the carrier aggregation is activated in thesecondary cell. That is, a UE is not always in an RRC connected state,but may make transition from an idle state to a connected state. In sucha case, a carrier aggregation for secondary cells may be additionallyapplied. In summary, data transmission and reception through a carrieraggregation of secondary cells are performed through the followingsteps.

-   -   1. Downlink or uplink data occurrence    -   2. A UE makes transition from an idle state to a connected state    -   3. A base station determines a carrier aggregation for secondary        cells    -   4. Data transmission and reception through a corresponding cell        after receiving a carrier aggregation activation signal for a        secondary cell    -   5. The UE makes transition to an idle state (after transition to        an inactive state or after the lapse of a given time)

Furthermore, in LTE, a carrier aggregation for secondary cells isconfigured through an RRC message, and the initial state of theconfigured cell is set as deactivation (off). A carrier aggregation fora corresponding cell is activated (on) through an MAC CE in which timingnecessary for a base station is delivered. A time delay occurs betweenthe transmission of the MAC CE and the occurrence of data transmissionand reception after a carrier is actually activated. The time delay isthe time taken for the following process.

-   -   1. MAC CE transmission delay    -   2. MAC CE processing time    -   3. UE RF synchronization and tuning time for a secondary cell    -   4. Actual transmission

If a UE makes transition from an idle state to a connected state, anoverall consumption delay time may be much great compared to the listedprocess. The reason for this is that a process for a UE to receive anRRC reconfiguration message needs to be first included.

FIG. 2F is a diagram illustrating an operation of performing a carrieraggregation upon transition from an inactive state to a connected state,which is proposed in the disclosure.

If a UE is in an inactive state in an LTE or NR system, a method usingUE context may be considered. That is, when the UE makes transition toan inactive state, a base station may indicate that the UE shouldmaintain a configuration for a secondary cell. That is, the base stationdetermines that a configuration for which secondary cells has to bemaintained, and delivers a corresponding list to the UE. The list may bethe same as or different from that of a configuration for secondarycells that the UE has received from the base station in a connectedstate. That is, the base station may provide a proper secondary cellconfiguration at timing in which the UE enters an inactive state. The UEthat has received the list and entered the inactive state rapidlyperforms a carrier aggregation to a secondary cell of the configuredlist if the UE makes transition to a connected state again. As a methodtherefor, the disclosure proposes two methods below.

1. Option 1

-   -   During a resume procedure, a UE performs an operation of        actively performing RF synchronization and tuning on all of        secondary cells/carriers included in a list configured in an RRC        message (RRC connection reconfiguration or RRC connection        release) in which a base station indicates transition to an        inactive state (e.g., receives paging or stores uplink data in a        buffer).    -   The base station immediately activates a carrier aggregation for        a given secondary cell through an MAC CE with respect to the UE        that has made transition to the RRC connected state.

2. Option 2

-   -   A base station explicitly configures a carrier aggregation for a        given secondary cell in a Resume message to indicate that a UE        should make transition from an inactive state to a connected        state (a secondary cell or multiple candidate secondary cells        for which a carrier aggregation will be activated may be        included).    -   The base station immediately activates a carrier aggregation for        a given secondary cell through an MAC CE with respect to the UE        that has made transition to the RRC connected state.

Both the methods have an advantage in that they can reduce a time delaynecessary for corresponding operation because a UE performs theoperation of performing RF synchronization and tuning on configuredsecondary cells. A detailed operation will be described through FIG. 2F.

Referring to FIG. 2F, if downlink data is present, at step 2 f-05, a UE2 f-01 may receive paging from abase station 2 f-02. Furthermore, atsteps 2 f-10 to 2 f-20, the UE 2 f-01 may perform a step forestablishing an RRC connection. That is, at step 2 f-10, the UE 2 f-01may transmit an RRC connection request message to the base station 2f-02. At step 2 f-15, the UE 2 f-01 may receive an RRC connection setupmessage from the base station 2 f-02. Furthermore, at step 2 f-20, theUE 2 f-01 may transmit an RRC connection setup complete message to thebase station 2 f-02. The step of receiving paging (step 2 f-05) may beomitted if data from the UE 2 f-01 occurs. At step 2 f-25, the UE 2 f-01makes transition to an RRC connected state through steps 2 f-05 to 2f-20. Thereafter, the base station 2 f-03 receives a UE capability fromthe UE 2 f-01, and may determine whether to configure secondary cellsfor a carrier aggregation in the corresponding UE. At steps 2 f-30 and 2f-35, the base station 2 f-03 may indicate a secondary cellconfiguration for a carrier aggregation in the UE 2 f-01 through an RRCreconfiguration procedure (the transmission and reception of an RRCconnection reconfiguration message and an RRC connection reconfigurationcomplete message). For example, it is assumed that setting values forsecondary cells Nos. 2, 3, 4, and 5 are included. Thereafter, the basestation 2 f-02 may determine actually necessary timing among theconfigured secondary cells, and may transmit, to the UE 2 f-01, an MACCE to indicate the activation of the carrier aggregation at step 2 f-40.For example, carrier aggregation activation for the secondary cells Nos.2, 3, and 4 may be indicated. Thereafter, the configured secondary cellsare activated, and data transmission and reception are performed throughthe corresponding cells.

Thereafter, at step 2 f-45, the base station 2 f-02 may indicate thatthe UE 2 f-01 should make transition to an inactive state for a cause,such as the absence of downlink data. An RRC connection reconfiguration,an RRC connection release message or a corresponding different RRCmessage may be used for the indication. For example, the RRC message mayinclude an indication for a configuration that needs to be maintained insecondary cells Nos. 2 and 3. The UE 2 f-01 may transmit, to the basestation 2 f-02, a confirm message (e.g., RRC connection reconfigurationcomplete message, RRC connection release complete message) for themessage at step 2 f-50, and may make transition to an inactive state atstep 2 f-55. Thereafter, at step 2 f-60, if downlink data is present,the UE 2 f-01 may receive paging from the base station 2 f-02.Furthermore, the UE may perform a step for establishing an RRCconnection. Accurately, the UE may perform a Resume procedure fortransition from an inactive state to a connected state. First, at step 2f-65, the UE 2 f-01 transmits a Resume request message (RRC connectionresume request message) to the base station 2 f-02. At step 2 f-70, theUE 2 f-01 receives a Resume message (RRC connection resume message) fromthe base station 2 f-02. The Resume message may include configurationinformation for carrier aggregation activation for secondary cells. Forexample, the Resume message may include carrier aggregationconfiguration information for a secondary cell No. 2. The informationmay be different from the information provided by the base station 2f-02 at step 2 f-45. Thereafter, at step 2 f-75, the UE 2 f-01 maynotify the base station 2 f-02 of Resume Complete, and may transmit amessage to request a connection reconfiguration. An RRC resume completemessage or an RRC connection reestablishment complete message or anotherRRC message including the information may be used for the message.

During the inactive state, the UE 2 f-01 performs each of the followingoperations according to the two methods proposed in the disclosure.

1. The UE 2 f-01 may perform an operation of matching RF synchronizationand tuning for the secondary cells configured by the base station 2 f-02at step 2 f-45.

2. The UE 2 f-01 may perform an operation of matching RF synchronizationand tuning for the secondary cells configured by the base station 2 f-02at step 2 f-70.

The UE 2 f-01 makes transition to the RRC connected state (2 f-80)through the processes. Thereafter, a carrier aggregation for givensecondary cells is activated through the MAC CE to indicate the carrieraggregation activation of the base station 2 f-02 (step 2 f-85). At step2 f-90, the UE performs data transmission and reception through acorresponding cell.

FIG. 2G is a diagram describing a given situation in which a secondarycell configuration is maintained in an inactive state, which is proposedin the disclosure.

Basically, when a UE makes transition from an inactive state or idlestate to a connected state, although a base station provides a carrieraggregation setting value for a given secondary cell, the UE cannotexpect the link characteristic of configured corresponding secondarycells. Accordingly, although the UE applies the configured correspondingsecondary cells, performance cannot be guaranteed. In the disclosure, itis assumed that secondary cells configured by a base station aresecondary cell present within the base station based on informationowned by the base station or configured if performance is guaranteed.Secondary cells will be configured by considering the condition whenthey are implemented in a network.

A situation to which the disclosure may be applied, that is, a basestation capable of configuring a secondary cell for a carrieraggregation may be listed as follows.

-   -   1. A base station that configures a secondary cell for a carrier        aggregation is a serving cell 2 g-10 that indicates an inactive        state in a UE    -   2. Base stations 2 g-10˜2 g-35 present within an RAN paging area    -   3. Base stations 2 g-10˜2 g-25 present within a newly defined        first cell group

The RAN paging area is a set of cells that share the UE context of a UEwhen the UE operates in an inactive state. A base station present withinthe corresponding area may indicate transition to a connected state withrespect to the UE 2 g-05 in the inactive state. The first cell groupincludes a serving cell that indicates the inactive state in the UE, andmay include one or more areas smaller than or equal to the RAN pagingarea. Furthermore, the RAN paging area and the newly defined first cellgroup need to be a set of cells capable of guaranteeing performance fora fast carrier aggregation activation configuration of the UE. That is,secondary cells configured by the base station include secondary cellspresent within the base station based on information owned by the basestation or include a set of cells configured when performance isguaranteed although a configured carrier aggregation is activatedalthough the UE is connected in a corresponding cell.

FIG. 2HA is a diagram illustrating the entire operation of a UE to whichthe disclosure is applied. FIG. 21113 is a diagram illustrating theentire operation of a UE to which the disclosure is applied.

The disclosure has an object of rapidly performing a carrier aggregationupon transition from an inactive state (RRC INACTIVE state) to an RRCconnected state, and provides several types of signaling and anoperation of a UE that receives the corresponding signaling.

At step 2 h-05, a UE identifies whether a message in which a basestation indicates transition to an inactive state includes a first SCellconfiguration list to indicate a carrier aggregation configuration. Thefirst SCell configuration list is a message included in an RRC messageto indicate deactivation, and indicates that a UE should perform an RFsynchronization and tuning operation on an SCell for a configured listeven after the UE makes transition to an inactive state. If the messageincludes the first SCell configuration list, at step 2 h-10, the UEmakes transition to an inactive state and performs an RF synchronizationand tuning operation on configured SCells. Thereafter, at step 2 h-15,the UE performs an RRC connection with the base station, that is, aResume operation, for a cause of the occurrence of uplink or downlinkdata. The operation is performed when the base station transmits an RRCResume message or an RRC reestablishment message. At step 2 h-20, the UEidentifies whether a second SCell configuration list including a carrieraggregation configuration for a given SCell has been included in themessage. The second SCell configuration list may be the same as ordifferent from the first SCell configuration list. If the second SCellconfiguration list is present, at step 2 h-25, the UE performs an RFsynchronization and tuning operation on cells included in thecorresponding SCell list. Thereafter, at step 2 h-30, the UE makestransition to an RRC connected state. At step 2 h-35, the UE mayreceive, from the base station, a MAC CE including a third SCellconfiguration list for carrier aggregation activation. Furthermore, atstep 2 h-40, the UE activates a corresponding cell and performs datatransmission and reception. If the second SCell configuration list isnot present in the message to indicate an RRC connection or Resume atstep 2 h-20, at step 2 h-45, the UE performs an RF synchronization andtuning operation on cells included in the first SCell configuration listreceived at step 2 h-05. Thereafter, at step 2 h-50, the UE makestransition to an RRC connected state. At step 2 h-55, the UE mayreceive, from the base station, a MAC CE including a third SCellconfiguration list for carrier aggregation activation. Furthermore, atstep 2 h-60, the UE activates a corresponding cell and performs datatransmission and reception.

If the first SCell configuration list is not present in the RRC messageto indicate deactivation at step 2 h-05, at step 2 h-65, the UE makestransition to an inactive state. At step 2 h-70, the UE performs an RRCconnection with the base station, that is, a Resume operation, for acause of the occurrence of uplink or downlink data. The operation isperformed when the base station transmits an RRC Resume message or anRRC re-establishment message. At step 2 h-75, the UE identifies whethera second SCell configuration list including a carrier aggregationconfiguration for a given SCell has been included in the message. If thesecond SCell configuration list is present, at step 2 h-80, the UEperforms an RF synchronization and tuning operation on cells included inthe corresponding SCell list. Thereafter, at step 2 h-85, the UE makestransition to an RRC connected state. At step 2 h-90, the UE mayreceive, from the base station, an MAC CE including a third SCellconfiguration list for carrier aggregation activation. Furthermore, atstep 2 h-95, the UE activates a corresponding cell and performs datatransmission and reception. If the second SCell configuration list isnot present in the message to indicate an RRC connection or Resume atstep 2 h-75, at step 2 h-100, the UE performs the existing operation inLTE. That is, the base station receives a Reconfiguration message againfrom the UE. The UE receives a configuration for an SCell, receives anMAC CE to indicate the activation of the corresponding SCell, performsRF synchronization and tuning, and then performs data transmission alongwith corresponding cells (steps 2 e-30˜2 e-40).

FIG. 2I is a block diagram illustrating an internal structure of a UE towhich the disclosure has been applied.

Referring to the figure, the UE includes a radio frequency (RF)processor 2 i-10, a baseband processor 2 i-20, a memory 2 i-30, and acontroller 2 i-40.

The RF processor 2 i-10 performs a function for transmitting andreceiving signals through a radio channel, such as the band conversion,amplification, etc. of a signal. That is, the RF processor 2 i-10up-converts a baseband signal received from the baseband processor 2i-20 into an RF band signal, transmits the RF band signal through anantenna, and down-converts an RF band signal received through theantenna into a baseband signal. For example, the RF processor 2 i-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital to analog convertor (DAC), and an analogto digital convertor (ADC). In FIG. 2I, only one antenna has beenillustrated, but the UE may include multiple antennas. Furthermore, theRF processor 2 i-10 may include multiple RF chains. Furthermore, the RFprocessor 2 i-10 may perform beamforming. For the beamforming, the RFprocessor 2 i-10 may adjust the phase and size of each of signalstransmitted/received through multiple antennas or antenna elements.Furthermore, the RF processor may perform MIMO. When the RF processorperforms the MIMO operation, it may receive multiple layers.

The baseband processor 2 i-20 performs a baseband signal and inter-bitstream conversion function based on the physical layer standard of asystem. For example, when data is transmitted, the baseband processor 2i-20 generates complex symbols by coding and modulating a transmissionbit stream. Furthermore, when data is received, the baseband processor 2i-20 reconstructs a reception bit stream from a baseband signal receivedfrom the RF processor 2 i-10 through demodulation and decoding. Forexample, if an orthogonal frequency division multiplexing (OFDM) schemeis applied, when data is transmitted, the baseband processor 2 i-20generates complex symbols by coding and modulating a transmission bitstream, maps the complex symbols to subcarriers, and then configuresOFDM symbols through an inverse fast Fourier transform (IFFT) operationand cyclic prefix (CP) insertion. Furthermore, when data is received,the baseband processor 2 i-20 segments a baseband signal received fromthe RF processor 2 i-10 in an OFDM symbol unit, reconstructs signalsmapped to subcarriers through a fast Fourier transform (FFT) operation,and reconstructs a reception bit stream through demodulation anddecoding.

The baseband processor 2 i-20 and the RF processor 2 i-10 transmit andreceive signals as described above. Accordingly, the baseband processor2 i-20 and the RF processor 2 i-10 may be called a transmitter, areceiver, a transceiver or a communication unit. Furthermore, at leastone of the baseband processor 2 i-20 and the RF processor 2 i-10 mayinclude multiple communication modules in order to support differentmultiple radio access technologies. Furthermore, at least one of thebaseband processor 2 i-20 and the RF processor 2 i-10 may includedifferent communication modules in order to process signals of differentfrequency bands. For example, the different radio access technologiesmay include a wireless LAN (e.g., IEEE 802.11), a cellular network(e.g., LTE), etc. Furthermore, the different frequency bands may includea super high frequency (SHF) (e.g., 2 NRHz, NRhz) band and a millimeterwave (e.g., 60 GHz) band.

The memory 2 i-30 stores data, such as a basic program, an applicationprogram, and configuration information for the operation of the UE. Inparticular, the memory 2 i-30 may store information related to a secondaccess node that performs wireless communication using a second radioaccess technology. The memory 2 i-30 provides stored data in response toa request from the controller 2 i-40.

The controller 2 i-40 controls an overall operation of the UE. Forexample, the controller 2 i-40 transmits/receives a signal through thebaseband processor 2 i-20 and the RF processor 2 i-10. Furthermore, thecontroller 2 i-40 writes data in the memory 2 i-40 and reads data fromthe memory 2 i-40. To this end, the controller 2 i-40 may include atleast one processor. For example, the controller 2 i-40 may include acommunication processor (CP) performing control for communication and anapplication processor (AP) controlling a higher layer, such as anapplication program.

FIG. 2J is a block diagram illustrating the configuration of a basestation according to the disclosure.

As illustrated in the figure, the base station is configured to includean RF processor 2 j-10, a baseband processor 2 j-20, a backhaulcommunication unit 2 j-30, a memory 2 j-40 and a controller 2 j-50.

The RF processor 2 j-10 performs a function for transmitting andreceiving signals through a radio channel, such as the band conversionand amplification of a signal. That is, the RF processor 2 j-10up-converts a baseband signal received from the baseband processor 2j-20 into an RF band signal, transmits the RF band signal through anantenna, and down-converts an RF band signal received through theantenna into a baseband signal. For example, the RF processor 2 j-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a DAC, and an ADC. In FIG. 1K, only one antennahas been illustrated, but the first access node may include multipleantennas. Furthermore, the RF processor 2 j-10 may include multiple RFchains. Furthermore, the RF processor 2 j-10 may perform beamforming.For the beamforming, the RF processor 2 j-10 may adjust the phase andsize of each of signals transmitted/received multiple antennas orantenna elements. The RF processor may perform a downlink MIMO operationby transmitting one or more layers.

The baseband processor 2 j-20 performs a baseband signal and inter-bitstream conversion function based on the physical layer standard of afirst radio access technology. For example, when data is transmitted,the baseband processor 2 j-20 generates complex symbols by coding andmodulating a transmission bit stream. Furthermore, when data isreceived, the baseband processor 2 j-20 reconstructs a reception bitstream from a baseband signal received from the RF processor 2 j-10through demodulation and decoding. For example, if the OFDM scheme isapplied, when data is transmitted, the baseband processor 2 j-20generates complex symbols by coding and modulating a transmission bitstream, maps the complex symbols to subcarriers, and configures OFDMsymbols through IFFT operation and CP insertion. Furthermore, when datais received, the baseband processor 2 j-20 segments a baseband signalreceived from the RF processor 2 j-10 in an OFDM symbol unit,reconstructs signals mapped to subcarriers through FFT operation, andthen reconstructs a reception bit stream through demodulation anddecoding. The baseband processor 2 j-20 and the RF processor 2 j-10transmit and receive signals as described above. Accordingly, thebaseband processor 2 j-20 and the RF processor 2 j-10 may be called atransmitter, a receiver, a transceiver, a communication unit or awireless communication unit.

The backhaul communication unit 2 j-30 provides an interface forperforming communication with other nodes within a network. That is, thebackhaul communication unit 2 j-30 physically converts a bit stream,transmitted from a primary base station to another node, for example, asecondary base station, a core network, etc., into a physical signal,and converts a physical signal, received from another node, into a bitstream.

The memory 2 j-40 stores data, such as a basic program, an applicationprogram, and configuration information for the operation of the basestation. Specifically, the memory 2 j-40 may store information on abearer allocated to an accessed UE and measurement results reported byan accessed UE. Furthermore, the memory 2 j-40 may store information,that is, a criterion by which whether to provide a UE with multipleconnections is determined. Furthermore, the memory 2 j-40 providesstored data in response to a request from the controller 2 j-50.

The controller 2 j-50 controls an overall operation of the primary basestation. For example, the controller 2 j-50 transmits/receives a signalthrough the baseband processor 2 j-20 and the RF processor 2 j-10 orthrough the backhaul communication unit 2 j-30. Furthermore, thecontroller 2 j-50 writes data in the memory 2 j-40 and reads data fromthe memory 2 j-40. To this end, the controller 2 j-50 may include atleast one processor.

The embodiments of the disclosure disclosed in this specification anddrawings have suggested given examples in order to easily describe thetechnical contents of the disclosure and to help understanding of thedisclosure, but are not intended to limit the scope of the disclosure.It is evident to a person having ordinary skill in the art to which thedisclosure pertains that other modified examples based on the technicalspirit of the disclosure are possible in addition to the disclosedembodiments.

The preferred embodiments of the disclosure have been disclosed in thisspecification and drawings. Although specific terms have been used inthis specification and drawings, they are used in common meanings inorder to easily describe the technical contents of the disclosure and tohelp understanding of the disclosure, but are not intended to limit thescope of the disclosure. It is evident to a person having ordinary skillin the art to which the disclosure pertains that other modified examplesbased on the technical spirit of the disclosure are possible in additionto the disclosed embodiments.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: receiving, from a basestation, a radio resource control (RRC) message to configure at leastone secondary cell (SCell) for the terminal; receiving, from the basestation, an RRC release message indicating a configuration for an RRCinactive state of the terminal; storing configuration information on theat least one SCell for the terminal based on the RRC release message;entering the RRC inactive state from an RRC connected state based on theRRC release message; receiving, from the base station, an RRC resumemessage to resume an RRC connection; identifying whether the RRC resumemessage includes information for a configuration of the at least oneSCell; maintaining the at least one SCell, in case that the RRC resumemessage includes the information for the configuration of the at leastone SCell; and entering the RRC connected state from the RRC inactivestate based on the RRC resume message.